Image reading devices of the type that allow optimal imaging distances, include a targeting scheme of some kind useful solely in aligning the image reader to the target, to obtain an optimal imaging distance from the target. Most of these techniques project a pattern onto the target from a targeting LED or laser diode. An aperture and IR light shaping optics are often used to project a pattern onto the target as an aid to the human operator to correctly position the image reader based on the targeting pattern.
The operator moves the image reader until targeting lines or dots converge at a predefined point, which relates to the point at which an acceptable image can be acquired. An acceptable image may be defined as one that contains sufficient resolution for post-processing. With this method, if the initial operating position is not correct it may be difficult for the operator to determine which direction the device must be moved in order to get into range. Further, with this method, the operator will perceive they can only capture an image at the predetermined distance at which the lines or dots converge, even though an acceptable image could potentially be acquired some distance before or beyond that point.
U.S. Pat. No. 6,385,352, which issued to Roustaei on May 7, 2002, details a technique whereby a cylindrical lens is positioned over the targeting LED's to project a vertical line to frame the target. This technique however does not disclose apparatus for shaping the light emitted from the targeting LED's or for compensating for the resulting growth caused by the magnification of the line as the image reader is moved too close, or the shrinking of the line as it is moved away.
US Patent Application Publication 2003/0019934, which was filed by Hunter on Mar. 7, 2002 and published on Jan. 30, 2003, discloses a method using an aperture positioned over the targeting LED's to project a line pattern onto the target. These lines however, are projected laterally (horizontally) and do not bound the target. With this technique, it would be difficult to intuit the direction to move the image reader, as the patterns simply form a line across the target. In an imaging solution, this technique is particularly unsuitable, as the human operator would have difficulty in aligning the centre of the target with the line pattern.
Therefore there is a need for a targeting system, which provides an operator with intuitive information on which direction to move the portable image capturing device in order to achieve a successful decode. It would also be desirable for the targeting system to provide this intuitive information within the parameters of the entire imaging range of the device.